How Much Bandwidth Does an IP Video Link Need?
Bandwidth problems are nearly always sizing problems. This is the arithmetic to do before the cable is pulled, not after the picture freezes.
- The number that matters is sustained uplink
- What actually sets the bitrate
- How pixel rate scales the requirement
- Streams per channel, not channels
- Protocol overhead and retransmission
- Headroom: the rule that prevents callbacks
- Storage follows from the same number
- Commissioning: measure, do not assume
- FAQ
The number that matters is sustained uplink
An encoder's bandwidth requirement is a sustained figure, not a peak one. A link that tests fine on a speed test and drops frames under a live stream is the classic symptom of sizing against the wrong number. What has to hold up is the continuous upstream rate at the encoder's own port, for as long as the event runs.
Two consequences follow. First, the constraint is asymmetric: the encoder's uplink is what matters, not the download figure on the venue's internet package. Second, it applies per site. Ten remote sites each pushing one stream do not share a bandwidth problem; each one has its own, and they only converge where the streams actually meet.
What actually sets the bitrate
Four inputs decide the number on the encoder, and they interact.
- Resolution and frame rate. Together these give the raw pixel rate, which is the single biggest driver.
- Codec. H.265 typically delivers comparable subjective quality at roughly 40 percent less bitrate than H.264 for the same content. The saving is real but it is not free: decoding H.265 places more demand on the player or decoder at the far end. The trade-off is set out in H.264 vs H.265.
- Content complexity. A static lecture capture and a sports broadcast at the same resolution do not need the same bitrate. Motion, fine detail and noise all cost bits; a talking head does not.
- Bitrate control. CBR (constant bitrate) holds the rate steady and is the right choice when the link has a hard ceiling. VBR (variable bitrate) lets the rate move with content and suits recording, where the ceiling is storage rather than the wire. Both are available on the encoder; the mechanism is explained in What Is Bitrate?.
The practical range is set by the hardware. Encoders in this class run a configurable bitrate range of roughly 16 kbit/s to 16 Mbit/s, with some models reaching 20 Mbit/s. That is the envelope; where inside it you land is a content decision made by testing.
How pixel rate scales the requirement
Rather than memorise per-resolution bitrate figures, work from the pixel rate, because bitrate tracks it closely for a given encoder and quality target. Pixel rate is resolution multiplied by frame rate, and it is pure arithmetic:
| Format | Pixel rate | Relative to 720P30 |
|---|---|---|
| 1280×720 @ 30 Hz | 27.6 Mpixel/s | 1.0× |
| 1920×1080 @ 30 Hz | 62.2 Mpixel/s | 2.3× |
| 1920×1080 @ 60 Hz | 124.4 Mpixel/s | 4.5× |
| 3840×2160 @ 30 Hz | 248.8 Mpixel/s | 9.0× |
The useful reading: 4K30 costs roughly twice what 1080P60 costs, and about nine times 720P30, before any codec saving is applied. Choose H.265 over H.264 and divide by roughly 1.7. That is enough to size a link without pretending to a precision that content complexity does not permit.
It also explains a common specification mistake. Asking for 4K when the content is fast-moving often produces a worse result than 1080P60 at the same bitrate, because the bits have to spread over four times the pixels. Where motion is the point, frame rate beats resolution. The resolution and frame-rate ceilings of a given model are listed on its product page — the ZY-EH1401, for instance, is specified at up to 3840×2160@30Hz or 1920×1080P@60Hz.
Streams per channel, not channels
The multiplier people forget is stream count. A dual-stream encoder outputs a main stream and a sub stream per input, each with its own resolution, bitrate and protocol. That is what lets one input feed both a recorder and a mobile preview without a second box.
But streams consume encoding and network resource, and the ceiling depends on resolution. On the ZY-EH1401 the figure is four streams per channel at 1080P and one stream per channel at 4K. Plan the link against what you will actually run, not against the headline stream count.
Multi-channel hardware multiplies again. The ZY-EH1304 takes four HDMI inputs and produces up to sixteen streams out of a single 1000M RJ45 port — which is precisely why that port is gigabit rather than fast Ethernet. A four-channel 4K deployment is a bandwidth planning exercise, not a product selection exercise.
Protocol overhead and retransmission
Encoded bitrate is not wire bitrate. Above the encoded payload sits transport framing, and if the transport retransmits, more again.
- Unicast delivery to N viewers costs N copies. Ten viewers of one 6 Mbit/s stream is 60 Mbit/s at the source.
- Multicast sends one copy and lets the network replicate it, which is why it is the correct answer for one-to-many distribution inside a LAN. The mechanism is covered in Multicast, Unicast and Broadcast Explained.
- SRT adds retransmission and error correction so a lossy public link stays watchable. You pay for that robustness in bandwidth, and the amount depends on how lossy the path is. Behaviour is described in What Is SRT?.
Treat 5 to 10 percent as a working allowance for framing, and treat retransmission as an unknown you measure on the real path rather than a number you add in advance.
Headroom: the rule that prevents callbacks
Size the link so the sustained load sits at around 70 percent of usable capacity, and confirm with a sustained test rather than a burst test. On a shared or public path, test at the hour the link will actually be used, not at 03:00.
Where the uplink cannot be guaranteed, the design answer is to stop depending on it. Recording locally at full quality while pushing a lower-bitrate stream upstream is the pattern that survives a bad day on the network. A dual-stream encoder does this in one box: main stream to the recorder, sub stream to the network.
Storage follows from the same number
Once the bitrate is fixed, storage is arithmetic:
Storage per hour ≈ bitrate (Mbit/s) ÷ 8 × 3600 ÷ 1024 GB. At 8 Mbit/s that is about 3.5 GB per hour per stream. Multiply by stream count and by hours, then add the retention period. Audio is small by comparison but not zero.
This is where VBR earns its keep for recording: a quiet scene costs fewer bits, and over a long retention window that adds up. The caution is predictability — with VBR, capacity planning has a range rather than a single figure, so budget against the upper end.
Commissioning: measure, do not assume
| Item | Pass criterion |
|---|---|
| Sustained uplink at the encoder port | Holds the configured bitrate for the full event duration, not just a speed test |
| Load against capacity | Sustained load around 70 percent of usable capacity, measured at the hour of use |
| Port speed | Gigabit link negotiated and confirmed, not auto-negotiated down to 100M |
| Stream count | Actual streams running at target resolution confirmed on the encoder status page |
| Lossy path behaviour | If SRT is used, loss and recovery observed and logged over a representative period |
| Recorder throughput | Recording keeps pace at the configured rate with all channels live |
Log the measured figures at handover. The next person to add a channel will need to know what the link is already carrying, and a recorded baseline is worth more than a recollection.
Where to start
ZY-EH1304 4-Channel 4K Encoder
Four HDMI inputs, up to sixteen streams, one 1000M uplink — the case where bandwidth planning decides the design.
Multi-channelZY-EH1401 4K Encoder with Display
Up to 3840×2160@30Hz or 1920×1080P@60Hz, dual stream, CBR/VBR 16 kbit/s to 16 Mbit/s, gigabit full-duplex port.
Single channel 4KZY-EH1308 8-Channel 4K Encoder
Eight HDMI inputs at up to 4K30 per channel, with two RJ45 ports for separating traffic.
Eight channelsZY-EH1411-1U 1U Rack Encoder
Single-channel 4K30 in a 1U chassis with on-unit display for reading status at the rack.
Rack installFAQ
What bitrate should I set for 4K30?
There is no universal figure, because content complexity dominates. Work from the pixel-rate relationship: 4K30 carries about nine times the pixel rate of 720P30, so for equivalent quality it needs a multiple of that stream's bitrate, divided by roughly 1.7 if you use H.265 rather than H.264. Then test it. Start inside the encoder's configured range, watch fast-motion content, and raise the rate until artefacts stop being visible.
Is H.265 always the better choice?
For bandwidth and storage, usually yes — comparable subjective quality at roughly 40 percent less bitrate. The cost is at the decoding end: older players, some set-top boxes and low-power clients handle H.265 less comfortably than H.264. Where the audience is unknown or the receiving device is fixed and old, H.264 remains the safer choice despite costing more bandwidth.
Should I use CBR or VBR?
CBR when the link has a hard ceiling, because it makes the load predictable and keeps you inside it. VBR when the ceiling is storage rather than the wire, because quiet content costs fewer bits and that compounds over a long retention window. Live streaming to a platform with a bandwidth-limited uplink is the classic CBR case; archival recording is the classic VBR case.
Why does my link test fine but the stream still stutters?
Usually because the test measured a burst rather than sustained throughput, or measured download rather than upload. An encoder needs continuous upstream capacity for the whole event. Test upstream specifically, run it for the duration the stream will actually run, and run it at the time of day the stream will run.
Do I need gigabit Ethernet for video?
For a single 1080P stream, fast Ethernet may be sufficient. For multi-channel 4K it is not: a four-channel 4K encoder can produce sixteen streams through one port, which is why models such as the ZY-EH1304 ship with a 1000M RJ45 interface. Check for a negotiated gigabit link during commissioning — an auto-negotiated 100M link is a common and easily missed cause of congestion.
Related reading
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